Tool Mentor: Profiling Java Memory Usage Using Rational Purify and Rational PurifyPlus (Windows)

Tool Mentors > Rational Purify Tool Mentors > Profiling Java Memory Usage Using Rational Purify and Rational PurifyPlus (Windows)

Purpose

This tool mentor describes how to use Rational Purify to profile and improve memory usage in a Java applet, class file, JAR file, or executable—all of which are referred to here as "Java programs". This tool mentor is applicable for use with systems running Microsoft Windows.

Purify Plus is a Rational product that includes Purify functionality.

To learn more about Purify, read Getting Started with Rational Purify or Getting Started with Rational PurifyPlus.

For step-by-step information about using Purify, see the Purify online Help.

Related Rational Unified Process information:

Activity: Implement Component, refer to the section titled "Evaluate the Code".
Activity: Perform Unit Tests, refer to the section titled "Execute Unit Test".

Overview

Purify helps you identify Java memory problems. Using Purify, you can determine:

how much memory your program is using
how much new memory your program consumes for a specific set of actions
what methods and objects in your program are consuming so much memory
which objects may be preventing unneeded objects from being garbage collected
where it would be advisable to force a garbage collection to improve performance

Tool Steps

To use Purify to profile Java memory usage:

Run your Java program under Purify and take a snapshot after it completes initialization
Execute code that may be leaking and take another snapshot
Compare the two snapshots to identify methods that may be leaking memory
Examine suspect methods for unneeded objects

1. Run your Java program under Purify and take a snapshot after it completes initialization

The first step in Purify'ing your Java program is to benchmark memory usage when your program has completed initialization and has reached a steady state.

Start Purify and run your program from the Purify interface. Purify intercepts messages related to memory usage from the Java virtual machine (JVM), and uses these messages to profile the memory your program is using. After your program has finished its initialization procedures, use the Purify snapshot command to benchmark memory usage at that moment. The snapshot is your basis for investigating how your program uses memory as it runs.

Tip: You can use the Purify Filter Manager to focus memory profiling on specific class files and methods.

For more information, look up the following in the Purify online Help index:

profiling memory usage (Java)
running programs (Java)
filter manager (Java)

2. Execute code that may be leaking and take another snapshot

With your program running under Purify, execute the parts of the program that you suspect are leaking memory. Purify displays a graph that shows changes in the amount of allocated memory. When you observe an increase in allocated memory, take another snapshot.

3. Compare the two snapshots to identify methods that may be leaking memory

When you have taken the second snapshot of your program's memory usage, exit your program and compare (or "diff") the two snapshots. Purify displays a call graph showing the methods that are responsible for the largest amounts of allocated memory. You can focus on specific methods within the call graph to investigate them more closely.

Purify also presents memory usage data for each method in a Function List View. You can sort the list on any of the data columns and view more detailed information for a method in a Function Detail window.

If the amount of memory allocated to a method is unexpectedly large, examine your source code and revise it, if necessary, to free memory when there is no longer a need for it.

For more information, look up the following topics in Purify online Help index:

comparing snapshots (Java)
finding leaked memory (Java)
call graph (Java)
function list view (Java)
function detail (Java)

4. Examine suspect methods for unneeded objects

Once you’ve identified methods that appear to have memory problems, analyze these methods at the object level. Look for objects that should be, but have not been, freed and garbage-collected, perhaps because other objects retain an unneeded reference to them.

You can examine objects in a method's Function Detail window, which lists all objects allocated by the method. You can also use the Object List View tab of the Data Browser window to view and sort all objects that are currently allocated.

For all details about a specific object, use the Object Detail window. This window includes a graph showing all objects in the "reference tree" to which the object belongs, as well as information about the object such as its size and the number of garbage collections it has survived. This window also displays an object dump that may contain references from the object to other objects.

Note that you cannot examine objects from within a "diff" dataset; you have to start with a snapshot or aggregate dataset.

For more information, look up the following in the Purify online Help index:

object list view (Java)
object detail window (Java)

Rational Unified Process